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Abstract

This paper presents the design and experimental study of a coupled-cavity laser based on the micromachining technology for wide tuning range and improved spectral purity. The core part of this design utilizes a deep-etched movable parabolic mirror to couple two identical Fabry-Pérot chips and thus allows the active adjustment of the cavity gap so as to optimize the mode selection and to increase the tuning range as well. In experiment, the laser achieves the single longitudinal mode output over 51.3 nm and an average side-mode-suppression ratio of 22 dB when the tuning current varies from 5.7–10.8 mA. The measured wavelength tuning speed is 1.2 µs and the single mode output is stable at any wavelength when the tuning current is varied within ±0.06 mA. Compared with the conventional fixed cavity gap coupled-cavity lasers, such design overcomes the phase mismatching and mode instability problems while maintaining the merit of high-speed wavelength tuning using electrical current.

Figures (8)

Mechanism of the wavelength tuning in the coupled-cavity laser, the solid and dashed lines correspond to the different injection current applied to the tuning chip. (a). Possible modes of the lasing chip; (b). possible modes of the tuning chip; (c). coincident modes of the coupled-cavity; (d). laser gain profile; and (e). coupled-cavity laser output spectrum.

Threshold gain modulation as a function of the wavelength. (a) Threshold gain versus the wavelength; and (b) shift of the threshold gain with the change of effective refractive index by the variation of the tuning current.

Comparison of the output spectra of the micromachined CCL in different states. (a) Original multi-mode output of the single FP chip; (b) single-mode output spectrum of the micromachined CCL when the cavity gap is optimal (i.e., d=d0); and (c) multi-mode spectrum of the micromachined CCL chip when the cavity gap is not optimal (d≠d0)